1. Field of the Invention
The present invention relates to a method and a device for controlling a silo unloader of the type comprising one or two electrical motors for driving a gathering apparatus located on the top of the bulk material stocked in the silo and a further electrical motor operating a winch to which is suspended the gathering apparatus to lower the gathering apparatus into the silo as the stocked material is unloaded.
More particularly, the present invention relates to a control method and device especially designed for protecting the motor(s) driving the gathering apparatus against possible overcurrents inherent to some operating conditions of the silo unloaded, which overcurrents often causes damages to the motor or mechanical failures of the gathering apparatus due to the supplementary torque generated by the motor when these overcurrents occur.
2. Background of the Invention
The gathering apparatuses which form part of the conventional silo unloaders used for unloading cylindrically shaped farm silos generally comprise an arm rotating around an axle located vertically in the middle of the silo, and having a length substantially equal to the radius of the silo. This arm is provided with a gathering chain or an endless screw feeding a blower or a similar device which evacuates the stocked material through a vertical corridor. The gathering apparatus is initially located on the top of the stocked bulk material and is gradually lowered as this material is unloaded. A winch to which is suspended the gathering apparatus and which is operated by an electrical motor is used for carrying out and controlling this lowering motion. It is to be noted that the expression &lt;&lt;material&gt;&gt; as used in the present specification means the silage or bulk feeding which is usually stocked in a farm silo.
The above-described conventional unloaders used for unloading farm silos have the disadvantage of operating with a constant lowering motion. The result of such an operation is that, when the material to be unloaded is compact or frozen, the arm becomes very difficult to operate and the electrical motor driving the gathering apparatus is subject to currents greater than the recommended ratings. This disadvantage occurs everytime the operator is busy or does not take into consideration the reading of the ammeter which indicates this overstepping and consequently, does not operate the manual commands for reversing or stopping the motor driving the winch to which the gathering apparatus is suspended. During these conditions of operation, the gathering apparatus is subject to severe mechanical loads which often result into mechanical or electrical failures causing extra costs of maintenance to the consumers and/or manufacturers who must increase the quality and consequently the cost of their product in order to meet with the requirements of such an improper operation.